Visualizer: make keypoint threshold configurable
Visualizer: make keypoint threshold configurable

Summary: Make the keypoint threshold a class member, so it can be changed.

Reviewed By: ppwwyyxx

Differential Revision: D30690598

fbshipit-source-id: 29499eaf12257e5bb4871ea318dc4ab5523d304e

facebookresearch/detectron2,facebookresearch/detectron2,facebookresearch/detectron2